Kevin, behind Scalebuildings4all sells reasonably priced, OO scale, home cast and painted buildings originally marketed by SD Mouldings. Fully 'assembled' and painted buildings come in at around £14 each. Though be warmed that the mill is a substantial rural building and as such pitches in at £21.
During the summer I built up a nice collection of buildings over several weeks, enabling me to create a typical stone Cotswold/Dales village. Kevin religiously refunds any excess postage costs and has proved himself to me to be one of the good guys on eBay.